Superconducting thin-films magnetically modulated

PORTLAND, Ore.—Superconductors have typically required bulk materials to transform into resistanceless conduction mode when cooled, but researchers have bucked that trend by fabricating thin films of nanowires at Brookhaven National Laboratory in cooperation with Israel's Bar-Ilan University.

Once fabricated, the scientists discovered that external magnetic fields could modulate the resistance of their nanowires, opening the future possibility of switching superconductivity on and off magnetically.

The thin-film material, which was cooled below about 30 degrees Kelvin (-405 degrees Fahrenheit), was composed of alternating layers of copper-oxide, lanthanum and strontium, deposited using molecular beam epitaxy. Electron-beam lithography was then used to etch the nanowires, measuring just 25 nanometers in diameter, into a pattern of two sized loops measuring just 150- and 500-nanometers.

A fragment of a superconducting thin film patterned with nano-loops measuring 150 nanometers on a side (small) and 500 nanometers on a side (large), where the nano wires making up each loop have a diameter of 25 nanometers.

Application of an externally increasing magnetic field was found to modulate the resistance of the material, instead make a linear change as was expected. As a result, the researchers hope to engineer a new type of superconducting thin film that enables the superconducting effect to be switched on and off magnetically.

Next, the researchers hope to unravel the mechanism that causes the observed frequency of resistance modulation, not only in pursuit of a new switchable superconducting material, but also to deepen the understanding of superconductivity. According to the researchers, their discovered response to an external magnetic field may narrow down the theories that are attempting to explain superconductivity, for instance potentially disqualifying the "stripes" theory.

Funding for the project was provided by the U.S. Department of Energy, the German Research Foundation and the Israel Ministry of Science.